CN116067534A - An all-paper-based hydrophobic piezoresistive sensor that can be used in high-humidity environments and underwater - Google Patents

Abstract

The invention provides an all-paper-based hydrophobic piezoresistive sensor that can be used in a high-humidity environment and underwater, and solves the problems of poor gas permeability and poor biocompatibility when the materials used in the flexible piezoresistive sensor used in underwater applications are in contact with the skin , and it is difficult to completely degrade, which is a technical problem that is not environmentally friendly. The piezoresistive sensor includes an upper packaging layer printed with an upper electrode, a sensing layer, and a lower packaging layer printed with a lower electrode, which are stacked in sequence, and the wires are drawn out as a whole and packaged with oily self-adhesive; the upper packaging layer and the lower packaging layer The layers are all hydrophobic and air-permeable paper; the sensing layer is double Z-shaped, which is paper impregnated with a conductive solution and has a machined surface.

Description

An all-paper-based hydrophobic piezoresistive sensor that can be used in high-humidity environments and underwater

technical field

The invention belongs to the technical field of piezoresistive sensors, in particular to an all-paper-based hydrophobic piezoresistive sensor that can be used in high-humidity environments and underwater.

Background technique

Flexible piezoresistive sensors, as a flexible electronic device, have attracted extensive attention due to their broad application prospects and ease of fabrication and operation. Flexible piezoresistive sensors can be attached to skin or clothing as electronic skin for continuous monitoring of human health. At the same time, it can also be used as a human-computer interaction interface, or help the robot perceive the external pressure of a certain part. Furthermore, due to its flexibility and lightness, it does not restrict the movement of man or machine. In recent years, flexible piezoresistive sensors have been widely studied in the acquisition of physiological signals such as respiratory monitoring and pulse detection. It has significant advantages such as mechanical flexibility, high sensitivity, fast response time, low cost, and simple processing. Flexible piezoresistive sensors can be divided into piezoelectric capacitors, piezoresistive, piezoelectric and triboelectric effect according to different working principles. Among them, the piezoresistive flexible piezoresistive sensor is favored by researchers because of its simple process, low energy consumption, high sensitivity in the low-voltage range, and simple signal acquisition. However, traditional flexible piezoresistive sensors use polymer materials such as PDMS, PET, etc. as substrates to achieve protection of the sensing layer and underwater application capabilities. These materials have the defects of poor air permeability and poor biocompatibility when in contact with the skin. In addition, discarded electronic equipment is often difficult to degrade, which brings a great burden to the environment.

Therefore, there is an urgent need to develop green flexible piezoresistive sensors that can be completely degraded and have good biocompatibility and have the ability to cope with complex changes in environmental humidity.

Contents of the invention

The purpose of the present invention is to solve the technical problems that the existing flexible piezoresistive sensors used in underwater applications have poor air permeability, poor biocompatibility, and are difficult to completely degrade and are not environmentally friendly when they are in contact with the skin. All-paper-based hydrophobic piezoresistive sensor for humidity environment and underwater applications.

To achieve the above object, the technical solution provided by the present invention is:

An all-paper-based hydrophobic piezoresistive sensor that can be used in a high-humidity environment and underwater. Encapsulation layer, lead out the wire as a whole and encapsulate it with oily self-adhesive;

The upper packaging layer and the lower packaging layer are both hydrophobic and air-permeable papers;

The sensing layer has multiple folded layers, preferably with the same number of folded layers, more angles can be produced, and it is paper impregnated with a conductive solution and has a machined surface.

Further, the hydrophobic air-permeable paper adopts filter paper modified with methyltrichlorosilane.

Further, the material of the upper electrode and the lower electrode is nano-silver ink or conductive gold ink.

Further, the conductive solution is configured with graphene/single-walled carbon nanotube composite material and deionized water.

Further, the paper with machined surface is kitchen paper;

The sensing layer is double Z-folded (that is, both sides of the composite paper are folded in a Z-shape).

Simultaneously, the present invention also provides the preparation method of above-mentioned all-paper-based hydrophobic piezoresistive sensor, and its special feature is, comprises the following steps:

1) Prepare hydrophobic air-permeable paper as packaging material;

2) Print the electrode material on the hydrophobic air-permeable paper, and cut it as needed to obtain the upper packaging layer printed with the upper electrode and the lower packaging layer printed with the lower electrode;

3) Prepare the sensing layer, fold it and place it between the upper encapsulation layer printed with the upper electrode and the lower encapsulation layer printed with the lower electrode, lead out the wires and then package it to obtain an all-paper-based hydrophobic piezoresistive sensor.

Further, step 1) is specifically:

Heat the filter paper and methyltrichlorosilane solution in a vacuum oven. Under the condition of 45-60°C for 30-60 minutes, the vapor of methyltrichlorosilane combines with the fibers of the paper, and finally obtains good hydrophobicity while retaining Hydrophobic breathable paper for paper breathability.

Further, step 2) is specifically:

2.1) Use the screen printing method to print electrodes on the hydrophobic air-permeable paper, and place them in an oven to volatilize the organic solvent, and finally form electrodes with good conductivity on the hydrophobic air-permeable paper; among them, the electrode material can use nano-silver ink For printing, put it in an oven and heat it at 150°C for 5 minutes to evaporate the organic solvent in the ink, and obtain a silver electrode accordingly;

2.2) Cutting according to needs to obtain an upper encapsulation layer printed with an upper electrode and a lower encapsulation layer printed with a lower electrode.

Further, step 3) is specifically:

3.1) Prepare a conductive solution, for example: stir the graphene/single-walled carbon nanotube composite material and deionized water at a mass ratio of 1:40 at room temperature for 25-30 minutes at a speed of 500-1000 rpm to obtain conductive solution;

3.2) The paper with the machined surface is placed in the conductive solution prepared in step 3.1) and dip-coated several times, then placed in an oven to volatilize the organic solvent to obtain a composite paper; if the above-mentioned graphene/single-walled carbon nanotubes are used The conductive solution prepared by the composite material and deionized water in a mass ratio of 1:40 can be dip-coated about 10 times, placed in an oven, and heated at 120°C for 10 minutes to volatilize the organic solvent in the solution to obtain a composite paper ; Of course, different proportions or conductive solutions configured with other printable conductive materials can also be used, and correspondingly, the number of dipping times will also be adjusted accordingly;

3.3) After the composite paper is folded in multiple layers (such as double "Z" folding, that is, the opposite sides of the composite paper are Z-folded), cut to a size smaller than the packaging layer;

3.4) Place the folded composite paper as the sensing layer between the upper encapsulation layer printed with the upper electrode and the lower encapsulation layer printed with the lower electrode, and use oily self-adhesive for encapsulation after leading out the wires to obtain a full paper base hydrophobic piezoresistive sensor.

Further, the size of the upper packaging layer and the lower packaging layer is 2×2 cm; the size of the sensing layer is 1.2×1.2 cm.

The present invention also provides an all-paper-based hydrophobic piezoresistive sensor array, which is special in that: a plurality of the above-mentioned all-paper-based hydrophobic piezoresistive sensors are arrayed on nanocellulose paper, which can realize pressure distribution recognition.

The advantages of the present invention are:

1. The all-paper base hydrophobic piezoresistive sensor of the present invention is to utilize the paper (such as: the kitchen paper that obtains easily, surface roughness is big) with the paper (for example: the composite of graphene and single-walled carbon nanotubes) that has machined surface material and deionized water configuration (conductive material) is folded as a sensing layer, and the overall preparation method has the advantages of simple and easy operation, green environmental protection and mass preparation.

2. The hydrophobic air-permeable paper prepared by the present invention has the advantages of easy preparation, low price, and eco-friendliness and environmental protection.

3. The intermediate sensing layer of the present invention is made of kitchen paper with a rougher surface after machining, soaked in graphene and single-walled carbon nanotube composite conductive material, and then folded. The raw materials are cheap and easy to obtain, and the production process is simple.

4. On the basis of the whole paper base, the sensor of the present invention can have the potential of being applied underwater and at the same time ensure the air permeability of wearing, without the need to use packaging materials that are not easy to degrade and have poor air permeability, such as polymers and petroleum-based materials. It has better biocompatibility and is more environmentally friendly.

5. The present invention uses paper as the encapsulation material, and can beautify the encapsulation layer by printing, so as to reduce the anxiety of the wearer during long-time wearing.

6. The piezoresistive sensor of the present invention has the advantages of high sensitivity and wide detection range.

7. The piezoresistive sensor of the present invention can detect some important human physiological signals and motion states.

8. The piezoresistive sensor of the present invention can perform pressure identification in high humidity conditions and shallow water environments.

9. The present invention can realize pressure distribution identification based on the piezoresistive sensor array.

Description of drawings

Figure 1 is a schematic diagram of the preparation and effect of the hydrophobic air-permeable paper.

Figure 2 is the SEM image of the hydrophobic air-permeable paper and the test of the contact angle of water droplets.

Figure 3 is the SEM image of the sensing layer material.

Figure 4 is a schematic diagram of the preparation process of the all-paper-based hydrophobic piezoresistive sensor.

Figure 5 is a photo of the cartoon pattern printed on the surface of the sensor.

Figure 6 shows the sensing performance of the prepared piezoresistive sensor.

Fig. 7 is a piezoresistive sensor for the detection of human physiological signals and motion.

Figure 8 shows the pressure response of the piezoresistive sensor in high humidity and water environments.

Fig. 9 is the preparation of piezoresistive sensor array for pressure distribution response.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment content of the present invention is described in further detail:

1) Preparation of the hydrophobic air-permeable paper encapsulation layer and electrodes of the all-paper-based hydrophobic piezoresistive sensor

Prepare hydrophobic air-permeable paper as the encapsulation layer of the piezoresistive sensor according to the method shown in Figure 1, and print electrodes on the hydrophobic air-permeable paper. The steps are as follows: choose filter paper as the packaging substrate, place it and 1ml trichloromethylsilane in a vacuum oven, heat to 45 degrees Celsius, after the methyltrichlorosilane volatilizes, a methyltrichlorosilane atmosphere is generated in the oven and mixed with the paper The fiber surface was bound and the final reaction was 30 minutes (Figure 1). Choose the method of screen printing to print the nano-silver conductive ink on the hydrophobic air-permeable paper as the electrode of the sensor. In the whole process, upper and lower packaging layers of the sensor with electrodes are prepared.

The prepared hydrophobic air-permeable paper has hydrophobicity and at the same time ensures the gap between the original fibers of the paper, so it will not affect the air permeability of the paper, which ensures that the final packaged sensor is hydrophobic while having Good air permeability (Figure 2).

The prepared hydrophobic and air-permeable paper can be printed with interesting cartoon patterns on its surface, so that the final sensor has an interesting appearance (2cm×2cm), which can relieve the wearer from wearing it for a long time to a certain extent. Anxiety during the process (Figure 5).

The electrodes are printed by screen printing, which ensures the potential of mass production of sensors. The final prepared electrode has good conductivity while ensuring flexibility.

2) Preparation of the sensing layer of the all-paper-based hydrophobic piezoresistive sensor

Firstly, graphene/single-walled carbon nanotubes: water was formulated into a solution at a ratio of 1:40, and a conductive solution with good stability and uniform distribution was obtained after magnetic stirring at room temperature for 30 minutes. Cut the selected kitchen paper with a machined surface into a suitable size, dip-coat it about 10 times, and heat it in an oven at 120 degrees Celsius for 10 minutes to volatilize the organic solvent to form a sensing layer with a black surface.

The prepared composite paper retains the machined surface and the inherent rough surface of the kitchen paper. At the same time, the fibers are randomly distributed, the composite conductive material is evenly attached to the fibers, and the single-walled carbon nanotubes are randomly distributed on the fibers (Figure 3).

The composite paper was folded in a double "Z" shape and cut into a size of 1.2cm×1.2cm as the final sensing layer.

3) Assemble the all-paper-based hydrophobic piezoresistive sensor

According to the flow diagram shown in Figure 4, a full paper-based hydrophobic piezoresistive sensor was prepared, and the steps were as follows: the composite kitchen paper prepared in step 2) was folded in a double "Z" shape, and cut into a size of 1.2cm×1.2cm, as final sensing layer. The upper and lower parts of the folded sensing layer are laminated with hydrophobic and air-permeable paper with printed electrodes and cartoon patterns (that is, the upper packaging layer and the lower packaging layer).

The prepared piezoresistive sensor for the first time enables the all-paper-based piezoresistive sensor to have the ability to be applied in high humidity and underwater scenes, while ensuring the gas permeability of the sensor. The sensor has high sensitivity and wide detection range in performance, and can be applied to the monitoring of human physiological signals and motion.

Figure 4 is a schematic diagram of the preparation of the all-paper-based piezoresistive sensor. It can be seen that the entire preparation process is simple and does not require complicated instruments. Fig. 5 is an appearance view of the prepared all-paper-based hydrophobic piezoresistive sensor. Figure 6 shows the sensing performance of the prepared all-paper-based hydrophobic piezoresistive sensor. The sensitivity of the obtained pressure sensor in the low-pressure area (0.03-0.6KPa) is 12.6KPa ^-1 , and the sensitivity in the high-pressure area (0.6-60.4KPa) is 4.3KPa ^-1 , which is better than most of the paper-based sensors reported so far.

Figure 7 shows the application of the all-paper-based hydrophobic piezoresistive sensor to detect the movement behavior of the human physiological signal machine. First, the detection of the sound is realized, and the sensor attached to the throat will generate a corresponding unique signal output for different words; followed by Monitoring of sitting posture; the sensor attached to the back will detect the muscle changes caused by the change of the wearer's sitting posture, and then output the corresponding signal. From the figure, we can see that different signal responses are generated when sitting straight and arched. Then, the sensor is attached to the wrist to detect the pulse. The age of the volunteer is 24 years old and the weight is 75 kg. The final detected pulse rate was 72 beats per minute. Finally, the walking detection is carried out. From the figure, we can see that different walking frequencies will produce different signals.

Figure 8 is the pressure response test of the application of the all-paper-based hydrophobic sensor in high humidity conditions and underwater environments. First of all, under high humidity conditions, we can see that the sensor has a good signal response to different pressure owners and is not affected by the humid environment. Then the underwater pressure test was carried out, and the pressure response after soaking the sensor in water for 30 minutes, it can be seen that the sensor still maintains an excellent pressure signal response. At the same time, the sensor is applied to the detection of underwater palm stretching and grasping motion.

At the same time, the present invention also adjusts the manufacturing process parameters of the piezoresistive sensor, uses different conductive materials and electrode materials for preparation, and obtains piezoresistive sensors that meet the requirements.

4) Preparation of all-paper-based piezoresistive sensor array

Firstly, a large-area transparent paper (nanocellulose paper) was prepared: a solution was prepared with sodium hydroxide, urea, and water at a ratio of 7:12:81 and stored at minus 20 degrees for 24 hours to ensure that the prepared solution was mixed with ice and water liquid. Place 4 grams of cotton linters in the above ice-water mixture under ice bath conditions and stir for 5-10 minutes with a mechanical stirring device at a speed of 1000 rpm, finally forming a viscous colloidal solution. Set the centrifuge at 10,000 rpm for 10 minutes to centrifuge the above viscous jelly liquid to finally obtain the supernatant. Use a glass rod to apply the supernatant to a glass plate, and place it in a certain volume of absolute ethanol for short-term cross-linking to form a stable gel-like film (it can avoid the thickness of the liquid when it is placed in a sulfuric acid solution). uneven, and to avoid surface wrinkling caused by water flow during placement), and then placed in 5% sulfuric acid solution for 5-10 minutes for replacement and final molding, until the glass plate is automatically peeled off. Soak the formed gel-like film in deionized water for 24 hours, then apply it on a glass plate, and stick it with adhesive tape (place it to wrinkle and crack during the drying process) and leave it at room temperature until it dries or in Dry in an oven (45°C). Finally, a transparent paper with a large area and excellent transparency and flatness is formed.

Connect electrodes and sensors on the transparent paper as shown in FIG. 9 , and finally make an all-paper-based sensor array. In Figure 9, the all-paper-based piezoresistive sensor identifies the pressure distribution of an externally applied object. It can be seen that our sensor array can clearly identify different external pressure distributions.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can easily think of various equivalents within the technical scope disclosed by the present invention. Modifications or replacements shall all fall within the protection scope of the present invention.

Claims (10)

1. An all-paper-based hydrophobic piezoresistive sensor that can be used in a high-humidity environment and underwater is characterized in that: it includes an upper packaging layer printed with an upper electrode, a sensing layer and a lower electrode printed with a lower electrode stacked in sequence. Encapsulation layer, lead out the wire as a whole and encapsulate it with oily self-adhesive; The upper packaging layer and the lower packaging layer are both hydrophobic and air-permeable papers; The sensing layer has multiple folded layers of paper impregnated with a conductive solution and has a machined surface. 2. The all-paper base hydrophobic piezoresistive sensor according to claim 1, characterized in that: The hydrophobic air-permeable paper adopts the filter paper modified by methyltrichlorosilane. 3. according to the described all-paper-based hydrophobic piezoresistive sensor of claim 1 or 2, it is characterized in that: The material of the upper electrode and the lower electrode is nano silver ink or conductive gold ink. 4. The all-paper base hydrophobic piezoresistive sensor according to claim 3, characterized in that: The conductive solution is configured by graphene/single-walled carbon nanotube composite material and deionized water. 5. The all-paper base hydrophobic piezoresistive sensor according to claim 4, characterized in that: The paper with machined surface is kitchen paper; The sensing layer is folded in a double "Z" shape. 6. the preparation method of the arbitrary described all-paper base hydrophobic piezoresistive sensor of claim 1-5, is characterized in that, comprises the following steps: 1) Prepare hydrophobic air-permeable paper as packaging material; 2) Print the electrode material on the hydrophobic air-permeable paper, and cut it as needed to obtain the upper packaging layer printed with the upper electrode and the lower packaging layer printed with the lower electrode; 3) Prepare the sensing layer, fold it and place it between the upper encapsulation layer printed with the upper electrode and the lower encapsulation layer printed with the lower electrode, lead out the wires and then package it to obtain an all-paper-based hydrophobic piezoresistive sensor. 7. according to the preparation method of the described all-paper base hydrophobic piezoresistive sensor of claim 6, it is characterized in that, step 1) is specially: Put the filter paper and methyltrichlorosilane solution in a vacuum oven to heat, and under the condition of 45-60°C for 30-60 minutes, the methyltrichlorosilane vapor combines with the fibers of the paper to obtain a hydrophobic and air-permeable paper. 8. according to the preparation method of the described all-paper-based hydrophobic piezoresistive sensor of claim 7, it is characterized in that, step 2) is specially: 2.1) Print electrodes on hydrophobic and air-permeable paper by screen printing method, and place them in an oven to volatilize the organic solvent; 2.2) Cutting according to needs to obtain an upper encapsulation layer printed with an upper electrode and a lower encapsulation layer printed with a lower electrode. 9. according to the preparation method of the described all-paper base hydrophobic piezoresistive sensor of claim 8, it is characterized in that, step 3) is specially: 3.1) preparing a conductive solution; 3.2) dipping the paper with the machined surface in the conductive solution prepared in step 3.1) for several times, and then placing it in an oven to volatilize the organic solvent to obtain a composite paper; 3.3) After the composite paper is folded in multiple layers, it is cut to a size smaller than that of the encapsulation layer; 3.4) Place the folded composite paper as the sensing layer between the upper encapsulation layer printed with the upper electrode and the lower encapsulation layer printed with the lower electrode, and use oily self-adhesive for encapsulation after leading out the wires to obtain a full paper base hydrophobic piezoresistive sensor. 10. An all-paper-based hydrophobic piezoresistive sensor array, characterized in that: a plurality of all-paper-based hydrophobic piezoresistive sensors according to any one of claims 1-5 are arrayed on the nanocellulose paper.

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